In general, battery charging is a complex electrochemical process in which the discharged electric energy must be replenished from an electric network. The quality of the charging process is critical to the health and longevity of batteries. As such, battery chargers need to be fitted with advanced controls to optimize charging and prolong battery life.
Conventional battery charging is done at low rates that return 60% to 70% of the battery's discharged energy within 6 hours, which brings the battery to about 80% to 90% state of charge (SOC). This is followed by an even lower rate of charge to bring the battery to 100% SOC in two to four hours. In total, a conventional charge cycle typically lasts 8 to 10 hours.
Rapid or fast charging is a new charging scheme that attempts to shorten the recharge time of batteries. Rapid charging greatly reduces the time it takes to bring the battery to a SOC of 80% to two hours or less. This reduction in time is accomplished by charging at a higher rate compared to conventional charging. While conventional charging recharges the battery at a rate of less than 10% to 15% of the amp-hour rating of the battery, rapid charging recharges the battery at a rate greater than 40%, resulting in more than a three-fold reduction in recharge time.
Rapid battery charging systems have been developed and are being offered by a number of manufacturers. However, these rapid charging systems have a number of drawbacks and limitations that have resulted in limited customer acceptance and penetration in the market place.
As a first example of the limitations of known rapid changing systems, most of these chargers are offered in a single power rating, namely 30 kW, 45 kW, or 60 kW. As such, customers with less than 30 kW power requirements, e.g. 10 kW or 20 kW, will have to pay extra for a higher power charging system (30 kW), that they will not be fully utilizing. In addition, customers with a 40 kW or 50 kW requirement settle for lower or higher rated battery chargers, namely 45 kW or 60 kW. This tradeoff makes such chargers more expensive from a customer perspective.
As a second example, all of these charging systems are non-modular and non-reconfigurable. As such, if a user's power needs increase at some point of time, the user would have to buy a new higher power charger to meet such need because the existing charger cannot be easily reconfigured for higher power operation.
As a third example, some of these charging systems support multiport operation but require extensive and complex installations as well as considerable infrastructure expenses, which must be covered by the customers. Typically, a conventional multiport charger consists of a central power server 10 along with a number of charging stations 11 as shown in FIG. 1. The multiport rapid charging system of FIG. 1 requires two levels of power conversion and control. The first is a main power server 10, which processes the AC power from the mains into distributed DC power, while the second are DC/DC charging ports 11 that charge individual battery powered systems (e.g., battery powered vehicles illustrated at 13 in FIG. 1).
FIG. 2 shows a block diagram of a typical multiport rapid charging system. In the conventional multiport charging system shown in FIG. 2, the main power server 10 can receive power from AC power lines at a 60 Hz transformer 14 which provides lower voltage AC power to an AC/DC converter 16. The converter 16 can be implemented in various ways, such as a passive rectifier followed by a DC/DC converter or as an active SCR rectifier. The converter 16 is controlled by a controller 18 through a gate drive and control 19. The DC output voltage from the converter 16 is applied to DC bus lines 20 that supplies DC power to the individual charging ports 11. Each of the charging ports 11 includes a DC to DC post regulator 22 and an output filter 23, with control being provided by a microprocessor and user interface 24 which receives signals indicating the output voltage and current from sensors 27 and which provides control signals to the regulator 22 through a gate drive and control circuit 28. The main system controller 18 also communicates with the microprocessor controller 24 in each of the individual ports 11 to provide overall system control. If rapid charging is to be available at all charging ports, the rating of the main power server must be quite high. If, however, the rating of the main power server 10 is limited, rapid charging will have to be trimmed when more battery powered systems, such as the vehicles 13, are charged simultaneously. In either case, the complexity and the cost of installing such charging systems are considerable.